CN103810756B - The method for drafting of self adaptive Loop subdivision curved surface based on irregular area - Google Patents

Abstract

The method for drafting of the Loop subdivision curved surface providing a kind of adaptivity based on irregular area of the present invention, this method for drafting adaptive mode based on irregular area, utilize the position calculating shader computations control vertex, relation according to current original dough sheet with the segmentation number of plies of adjacent original dough sheet, by the sub-dough sheet that irregular original patch division is several rules, trigonometric framework lattice are reconstructed, drawn by tessellation tinter again and obtain corresponding dough sheet, can effectively eliminate T crack.Tessellation tinter can be used to paint accurately by segmentation and be calculated the position on each layer summit in trigonometric framework lattice, the most all calculated summits are all identical with limit L oop subdivision curved surface with normal vector, and the drafting of hardware tessellation tinter, solve huge internal memory and the bandwidth problem of Global Subdivision method, it is possible to reach real-time accurate Drawing Loop subdivision curved surface.

Description

The method for drafting of self adaptive Loop subdivision curved surface based on irregular area

Technical field

The present invention relates to computer graphics subdivision curved surface field of drawing, be specifically related to a kind of based on The method for drafting of the Loop subdivision curved surface of the adaptivity of irregular area.

Background technology

Subdivision curved surface, in field of Computer Graphics, the grid for arbitrary topology creates smooth Curved surface.Subdivision curved surface is defined as the calculating of an infinite thinning process.Initial by repeatedly refining Polygonal mesh, the subdivision curved surface that a series of grid tends to final can be produced.Each new What refinement step generation one was new has more polygon element and more smooth network.Loop Subdivision curved surface is as wherein comparing a representative segmentation Strategy, at electronic game, electricity It is widely used in the application such as shadow making and finite element simulation, sees C.Loop, Smooth subdivision surfaces based on triangles,Master’s thesis,Dept.of Math., Univ.of Utah(1987).Loop subdivision curved surface is the triangle Controling network for arbitrary topology Lattice design, it is different from Catmull-Clark subdivision curved surface, sees E.Catmull, J.Clark, Recursively generated b-spline surfaces on arbitrary topological meshes, Computer-Aided Design10(6)(1978)350–355。

Traditional subdivision curved surface is according to subdivision rules, and cyclically micro-stepping control grid computing draws 's.Although this method is easily achieved on the GPU in the present age.But, exponential increase Internal memory occupancy volume and volume of transmitted data can be serious affect operational efficiency.Along with DirectX11 The appearance of API, hardware tessellation tinter therein, can be in GPU stream multiprocessing, directly Connect calculating, generate, draw the geometry of segmentation, reach to avoid the internal memory input and output of high cost, Draw the purpose of the high-quality surface-rendering of fine geometric detail, see Microsoft Corporation,Direct3D11Features, http://msdn.microsoft.com/en-us/library/ff476342(VS.85).aspx(2009).But It is that hardware tessellation draws curved surface and calculates by dough sheet.Although it can be used in directly Computation rule dough sheet, but for such as singular vertex, accurate sharp-pointed folding line and with different levels editor are so Irregular area, it is impossible to directly calculate.

Current existing Loop subdivision method for drafting is divided into three major types.First, Global Subdivision Method.Such method is realized by the segmentation that input controls grid circulation of the overall situation.This type of side The memory consumption of method is with the summit quantity linear increase generated.Owing to the bandwidth of GPU limits, Cause the degradation of performance, see L.Shiue, I.Jones, J.Peters, A realtimegpu subdivision kernel,ACM Transactions on Graphics24(3)(2005) 1010–1015.Second, direct calculation method.Such method is the segmentation square to subdivision curved surface The eigenmatrix analytical analysis of battle array, directly calculates and solves subdivision curved surface, see J.Stam, Evaluation of Loop subdivision surfaces,in:ACM SIGGRAPH99 Course Notes#37,SIGGRAPH’99,ACM,New York,NY,USA,1999, pp.111–125.Although this type of method easily realizes on GPU, but due to substantial amounts of program Code branch, causes runnability poor.Additionally, such method needs singular point to separate, because of This, need to do the initial grid that controls once to the pre-segmentation of twice, the control after so processing The summit of grid processed and dough sheet quantity are all by substantial increase；And, such method cannot process and make Accurate sharp-pointed folding line that type is common and editing by different level.Finally, approximate algorithm based on dough sheet. It is to find a solution approaching irregular area that such algorithm is considered carefully substantially, improves and draws efficiency, Sacrifice rendering quality.Such method utilizes hardware tessellation tinter to draw subdivision curved surface, See document G.Li, C.Ren, J.Zhang, W.Ma, Approximation of Loop subdivision surfaces for fast rendering,IEEE Transactions on Visualization and Computer Graphics17(4)(2011)。

Summary of the invention

For the deficiencies in the prior art, the invention provides a kind of based on irregular area adaptive GPU is answered to draw Loop subdivision surface methodology.

A kind of method for drafting of the Loop subdivision curved surface of adaptivity based on irregular area, Including:

(1) input trigonometric framework lattice, and set the maximum segmentation number of plies and Global Subdivision parameter；

(2) determine the irregular area of trigonometric framework lattice, and using this irregular area as The level 0 topological structure of trigonometric framework lattice, generates triangle according to level 0 topological structure and controls The level 0 segmentation look-up table of grid, builds trigonometric framework lattice according to level 0 segmentation look-up table Ground floor topological structure, and according to ground floor topological structure generate trigonometric framework lattice first Layer segmentation look-up table；

(3) recursion successively, obtains the n-th layer segmentation of trigonometric framework lattice search until building Table and n-th layer topological structure, wherein n is equal to the maximum segmentation number of plies set；

(4) position of each layer segmentation look-up table and level 0 control vertex is uploaded to GPU, The tinter that calculates of GPU segments look-up table and the position of last layer control vertex according to each layer, It is calculated the position of each layer control vertex successively；

(5) control of each original dough sheet in this topological structure is constructed according to each etale topology structure Dough sheet controls dough sheet as this layer, and determines that each controls the parameter field of dough sheet, specific as follows:

(5-1) will be each according to the segmentation number of plies residing for each original dough sheet in described topological structure Individual original dough sheet is divided into ordinary dough sheet and non-trivial dough sheet:

If the segmentation number of plies of the adjacent original dough sheet in the limit of current original dough sheet is respectively less than or is equal to work as The segmentation number of plies of front original dough sheet, the most current original dough sheet is ordinary dough sheet,

Otherwise, current original dough sheet is non-trivial dough sheet；

If (5-2) current original dough sheet is ordinary dough sheet, then with a ring of current original dough sheet The vertex index of neighborhood is as the control dough sheet of current original dough sheet, and determines this control dough sheet Parameter field；

If current original dough sheet is non-trivial dough sheet, then proceed as follows:

(5-21) ought more than the segmentation number of plies of current original dough sheet according to the adjacent original dough sheet in limit Front original dough sheet is divided into some sub-dough sheets,

(5-22) using the vertex index of a ring neighborhood of current original dough sheet as each sub-dough sheet Control dough sheet, and determine each control dough sheet parameter field；

(6) currently segment the number of plies according to Global Subdivision parameter determination, control according to each layer respectively The position on summit, each layer control dough sheet and each parameter field of dough sheet that controls by tessellation Tinter drafting level 0 dough sheet is to g_depth aspect sheet, and g_depth is for currently segmenting the number of plies.

In step (1), the trigonometric framework lattice of input include the control vertex of level 0.

Described step (2), step (3) and step (5) can be that off-line is carried out.

Topological structure structure comprises each original dough sheet, each dough sheet is connected with each other, Bian Xiang Proximal surface sheet refers to that the dough sheet sharing limit (having common edge) with this dough sheet becomes the adjacent dough sheet in limit.

The method for drafting intermediate cam of the Loop subdivision curved surface of the present invention controls grid, maximum segmentation The number of plies and Global Subdivision parameter are set by the user, wherein trigonometric framework lattice and the maximum segmentation number of plies The drawing process of Loop subdivision curved surface typically no longer adjusts, and Global Subdivision parameter exists In the drawing process of Loop subdivision curved surface, user can need to adjust in real time according to display.

Segmentation look-up table and the input that the method for drafting of the Loop subdivision curved surface of the present invention uses The geometry of trigonometric framework lattice is unrelated, and at the such triangle gridding of similar curved editor or animation Keep in topologically invariant application, the generation of this segmentation look-up table and upload and only need once, to change Need not regenerate and upload segmentation look-up table after becoming Global Subdivision parameter.

The drafting side of the Loop subdivision curved surface of the adaptivity based on irregular area of the present invention Method, adaptive mode based on irregular area, utilize and calculate tinter parallel computation control top The position of point, utilizes tessellation tinter to draw dough sheet.By utilizing, GPU's is parallel Disposal ability, solves huge internal memory and the bandwidth problem of Global Subdivision method.It addition, Tessellation tinter can only the dough sheet of direct accurate Drawing regular domain, but due to may phase Proximal surface sheet is on different subdivision of reservoir, directly draws dough sheet meeting according to tessellation tinter T-shaped crack there is, subdivision of reservoir according to current original dough sheet with adjacent original dough sheet in the present invention The relation of number, is some sub-dough sheets by irregular original patch division, then according to sub-face Sheet reconstruct trigonometric framework lattice, directly structure there will be T-shaped crack, it is impossible to (former with generatrix sheet Beginning dough sheet) it is that unit is drawn, it is necessary to draw in units of sub-dough sheet, then by tessellation Color device is drawn and is obtained corresponding dough sheet, can effectively eliminate T crack.

In described step (1), the maximum segmentation number of plies and Global Subdivision parameter meet following condition:

1.0≤g_tessfactor≤2ⁿ,

Wherein, g_tessfactor is Global Subdivision parameter, and n is the maximum segmentation number of plies.

The maximum segmentation number of plies is equivalent to a constraint, and user sets as required, in actual application N is less than 8.

Described irregular area is the singular point of trigonometric framework lattice, half acute vertex and layering Secondary in-edit.Generally trigonometric framework lattice with singular point, half acute vertex and are edited by different level Point, these points are irregular area, and constitute the level 0 topology knot of these trigonometric framework lattice Structure.

Singular point degree of referring to is not the summit of 6.

Half acute vertex refers to that each limit can be referred to by user on the trigonometric framework lattice of input A fixed sharp-pointed value, represents the acuity after the segmentation of this limit.If one the sharp-pointed value on limit is not Zero, then this limit is half sharp edge.If the limit of a summit connection is not zero containing sharp-pointed value Limit, then this point is half sharp point, the subacute meaning be this sharp-pointed value can be non-integer.

In-edit refers to according to moulding needs by different level, to trigonometric framework on difference segmentation level Lattice do the point edited, and the Limit Surface of Loop subdivision curved surface is to be made up of four box splines, removes Around singular point, it is be made up of an infinite number of four box spline curye surfaces.

Described segmentation table includes edge point table and point table,

Described edge point table is for recording in irregular area adjacent the two of each limit, edge point place The index on four summits of individual triangle；

Described some point table is for recording the index on each summit in irregular area, and each pushes up The degree of point, and a ring neighborhood vertex index on each summit and the original position on a ring neighborhood summit.

During each step of Loop subdivision curved surface is segmented, need controlling each of grid Bar limit and summit are segmented.Segmenting the summit obtained on limit is edge point, and opposite vertexes segmentation obtains Summit be referred to as some a point.

With a summit with an interconnective point in limit, become a ring neighborhood summit on this summit.

In edge point table and some point table, each content of record is stored respectively in corresponding caching, top The index of point is corresponding to indexed cache, in degree degree of the being stored in caching on summit, a ring neighborhood summit Original position use side-play amount represent, this side-play amount be stored in side-play amount caching in.

Described control vertex includes edge point and summit.

During the position of the control vertex calculating each layer in described step (4) in calculating tinter Being respectively provided with edge point thread and some point thread, described edge point thread is used for calculating the position of edge point, Described some point thread is for calculating the position on summit.

When calculating some point, from indexed cache, obtain this vertex index by a some thread, from degree caching Read the degree on this summit, obtain this summit one ring neighborhood vertex index by side-play amount caching and initiate Position, is starting point from this position, reads several (equal with this Vertex Degree) vertex index, And then obtain the index on a ring neighborhood summit on this summit, so, obtain all vertex index, Employing list of references: C.Loop, Smooth subdivision surfaces based on triangles, Master ' s thesis, Dept.of Math., Univ.of Utah (1987). in the method reported for work, meter Point coordinates is put in calculation accordingly.In like manner, the coordinate of available corresponding edge point.

Described step (5-21) including:

If a the adjacent original dough sheet in () only one of which limit is more than the segmentation number of plies of current original dough sheet, With the adjacent original dough sheet in this limit and the midpoint of the common edge of current original dough sheet with this is the most original In dough sheet, the line on the summit that this common edge is relative is cut-off rule, is split as by current original dough sheet Two sub-dough sheets；

If b () has two adjacent original dough sheets in limit segmentation number of plies more than current original dough sheet, With the line at two adjacent original dough sheets in limit and the midpoint of the common edge of current original dough sheet and times The meaning midpoint of one common edge and the line relative with this common edge be cut-off rule will be the most original Dough sheet is split as three sub-dough sheets；

If c () has three adjacent original dough sheets in limit segmentation number of plies more than current original dough sheet, With the line two-by-two at the midpoint on three limits of current original dough sheet as cut-off rule, will the most original Sheet is split as four sub-dough sheets.

Described step (6) comprises the following steps:

(6-1) according to formula:

Determining and currently segment the number of plies, wherein g_depth is for currently to segment the number of plies, and g_tessfactor is Global Subdivision parameter,Represent log₂G_tessfactor rounds up；

(6-2) according to formula:

tessfactor_i+1=tessfactor_i/ 2,

Calculate the subdivision parameter of i+1 layer, wherein tessfactor_iIt is the subdivision parameter of i-th layer, I=0,1 ..., g_depth, wherein tessfactor₀=g_tessfactor；

(6-3) based on four box spline basic functions, according to subdivision parameter, the control of each layer Summit, control dough sheet and each parameter field controlling dough sheet draw the dough sheet of equivalent layer.

The subdivision parameter of later layer is determined by the subdivision parameter of preceding layer, later layer in the present invention Subdivision parameter be the twice of subdivision parameter of preceding layer.After obtaining the subdivision parameter of each layer, Use four box spline basic functions can draw the dough sheet obtaining equivalent layer.After often segmenting once Control grid to can be understood as being subdivided once, then subdivision parameter halves.

Compared with the method for drafting of existing Loop subdivision curved surface, the Loop of the present invention is thin The method for drafting of point curved surface adaptive mode by irregular area, according to irregular dough sheet Type, by some the sub-dough sheets that are divided into of irregular dough sheet, then with the sub-dough sheet life obtained The control dough sheet becoming these trigonometric framework lattice carries out dough sheet drafting.Can be used by segmentation Tessellation tinter is painted and is accurately calculated the position on each layer summit in trigonometric framework lattice, The most all calculated summits are all identical with limit L oop subdivision curved surface with normal vector, and Hardware tessellation tinter is drawn, and the huge internal memory and the bandwidth that solve Global Subdivision method are asked Topic, it is possible to reach real-time accurate Drawing Loop subdivision curved surface.

Accompanying drawing explanation

Fig. 1 is the flow chart of the method for drafting of the Loop subdivision curved surface of the present invention；

Fig. 2 is method for splitting and the determination schematic diagram of parameter field of raw frames.

Detailed description of the invention

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

A kind of self adaptation GPU based on irregular area draws Loop subdivision surface methodology, bag Include following steps:

(1) input trigonometric framework lattice, and set the maximum segmentation number of plies and Global Subdivision parameter, And the maximum segmentation number of plies and Global Subdivision parameter meet following condition:

1.0≤g_tessfactor≤2ⁿ,

Wherein, g_tessfactor is Global Subdivision parameter, and n is the maximum segmentation number of plies (this enforcement G_tessfactor=1.0 in example, n=8).

(2) determine the irregular area of trigonometric framework lattice, and using this irregular area as The level 0 topological structure of trigonometric framework lattice, generates triangle according to level 0 topological structure and controls The level 0 segmentation look-up table of grid, builds trigonometric framework lattice according to level 0 segmentation look-up table Ground floor topological structure, and according to ground floor topological structure generate trigonometric framework lattice first Layer segmentation look-up table.

Irregular area is the singular point of trigonometric framework lattice, half acute vertex and edits by different level Point.In the present embodiment: singular point degree of referring to is not the summit of 6, half acute vertex refers to connection Bian Zhongyou is sharply worth the summit on the limit being not zero；In-edit refers to according to moulding needs by different level, On different segmentation levels, trigonometric framework lattice are done the point edited.

(3) recursion successively, obtains the n-th layer segmentation of trigonometric framework lattice search until building Table and n-th layer topological structure, wherein n is equal to the maximum segmentation number of plies set；

Segmentation look-up table includes edge point table and some point table, and edge point table is used for recording in irregular area The index on four summits of adjacent two trianglees on each limit, edge point place；Point point table is used for remembering The index on each summit in record irregular area, the degree on each summit, and the one of each summit Ring neighborhood vertex index and the original position on a ring neighborhood summit.

(4) position of each layer segmentation look-up table and level 0 control vertex is uploaded to GPU, The tinter that calculates of GPU segments look-up table and the position of last layer control vertex according to each layer, It is calculated the position of each layer control vertex successively.

(5) control of each original dough sheet in this topological structure is constructed according to each etale topology structure Dough sheet controls dough sheet as this layer, and determines that each controls the parameter field of dough sheet, specific as follows:

(5-1) will be each according to the segmentation number of plies residing for each original dough sheet in described topological structure Individual original dough sheet is divided into ordinary dough sheet and non-trivial dough sheet:

If the segmentation number of plies of the adjacent original dough sheet in the limit of current original dough sheet is respectively less than or is equal to work as The segmentation number of plies of front original dough sheet, the most current original dough sheet is ordinary dough sheet,

Otherwise, current original dough sheet is non-trivial dough sheet；

If (5-2) current original dough sheet is ordinary dough sheet, then with a ring of current original dough sheet The vertex index of neighborhood is as the control dough sheet of current original dough sheet, and determines this control dough sheet Parameter field；

If current original dough sheet is non-trivial dough sheet, then proceed as follows:

(5-21) ought more than the segmentation number of plies of current original dough sheet according to the adjacent original dough sheet in limit Front original dough sheet is divided into some sub-dough sheets, specific as follows:

If a the adjacent original dough sheet in () only one of which limit is more than the segmentation number of plies of current original dough sheet, With the adjacent original dough sheet in this limit and the midpoint of the common edge of current original dough sheet with this is the most original In dough sheet, the line on the summit that this common edge is relative is cut-off rule, is split as by current original dough sheet Two sub-dough sheets；

If b () has two adjacent original dough sheets in limit segmentation number of plies more than current original dough sheet, With the line at two adjacent original dough sheets in limit and the midpoint of the common edge of current original dough sheet and times The meaning midpoint of one common edge and the line relative with this common edge be cut-off rule will be the most original Dough sheet is split as three sub-dough sheets；

If c () has three adjacent original dough sheets in limit segmentation number of plies more than current original dough sheet, With the line two-by-two at the midpoint on three limits of current original dough sheet as cut-off rule, will the most original Sheet is split as four sub-dough sheets.

(5-22) using the vertex index of a ring neighborhood of current original dough sheet as each sub-dough sheet Control dough sheet, and determine each control dough sheet parameter field.

The basis of the parameter field controlling dough sheet of each sub-dough sheet of ordinary dough sheet in the present embodiment The computational methods of barycentric coodinates determine.

In the present embodiment non-trivial dough sheet control dough sheet segmentation rule, and segmentation after each The determination method of the parameter field of sub-dough sheet as in figure 2 it is shown, in figure dotted line represent cut-off rule, 1., 2., 3. and 4. it is the numbering of sub-dough sheet.

As shown in Figure 2 (a) shows, if the adjacent original dough sheet in only one of which limit is more than the most original The segmentation number of plies of sheet, then be split as the sub-dough sheet of two shown in Fig. 2 (a) by current original dough sheet.

1. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_1^a=\left\{(u,v)\right|u\∈\left[\mathrm{0,1}\right],v\∈[\frac{1}{2}(1-u),1]\};$

2. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_2^a=\left\{(u,v)\right|u\∈\left[\mathrm{0,1}\right],v\∈[0,\frac{1}{2}(1-u)]\}.$

As shown in Fig. 2 (b), if having two adjacent original dough sheets in limit more than current original dough sheet The segmentation number of plies, then current original dough sheet is split as three sub-dough sheets, wherein:

1. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_1^b=\left\{(u,v)\right|u\∈\left[\mathrm{0,1}\right],v\∈[\frac{1}{2}(1-u),1]\};$

2. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_2^b=\left\{(u,v)\right|u\∈[0,\frac{1}{2}],v\∈[\frac{1}{2}-u,\frac{1}{2}(1-u)]\}\∪\{(u,v)|u\∈[\frac{1}{2},1],v\∈[0,\frac{1}{2}(1-u)\left]\right\};$

3. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_3^b=\left\{(u,v)\right|u\∈[0,\frac{1}{2}],v\∈[0,\frac{1}{2}-u]\}.$

As shown in Figure 2 (c), if having three adjacent original dough sheets in limit more than current original dough sheet The segmentation number of plies, then current original dough sheet is split as four sub-dough sheets.Wherein:

1. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_1^c=\left\{(u,v)\right|u\∈[\mathrm{0,1}-v],v\∈[\frac{1}{2},1]\};$

2. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_2^c=\left\{(u,v)\right|u\∈[0,\frac{1}{2}],v\∈[\frac{1}{2}-u,\frac{1}{2}]\};$

3. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_3^c=\left\{(u,v)\right|u\∈[0,\frac{1}{2}],v\∈[0,\frac{1}{2}-u]\};$

4. the parameter field of work song dough sheet is:

${\mathrm{\Ω}}_4^c=\left\{(u,v)\right|u\∈[\frac{1}{2},1],v\∈[\mathrm{0,1}-u]\}.$

(6) currently segment the number of plies according to Global Subdivision parameter determination, control according to each layer respectively The position on summit, each layer control dough sheet and each parameter field of dough sheet that controls by tessellation Tinter drafting level 0 dough sheet is to g_depth aspect sheet, and g_depth is for currently segmenting the number of plies. Specifically include procedure below:

(6-1) according to formula:

Determining and currently segment the number of plies, wherein g_depth is for currently to segment the number of plies, and g_tessfactor is Global Subdivision parameter,Represent log₂G_tessfactor rounds up；

(6-2) according to formula:

tessfactor_i+1=tessfactor_i/ 2,

Calculate the subdivision parameter of i+1 layer, wherein tessfactor_iIt is the subdivision parameter of i-th layer, I=0,1 ..., g_depth, wherein tessfactor₀=g_tessfactor；

(6-3) based on four box spline basic functions, according to subdivision parameter, the control of each layer Summit, control dough sheet and each parameter field controlling dough sheet draw the dough sheet of equivalent layer.

The above, the only detailed description of the invention of the present invention, but protection scope of the present invention is also Being not limited to this, any those familiar with the art is at the technology model that the invention discloses In enclosing, the change that can readily occur in or replacement, all should contain within protection scope of the present invention.

Claims (8)

1. a method for drafting for the Loop subdivision curved surface of adaptivity based on irregular area, It is characterized in that, comprise the steps:

(1) input trigonometric framework lattice, and set the maximum segmentation number of plies and Global Subdivision parameter；

(2) determine the irregular area of trigonometric framework lattice, and using this irregular area as The level 0 topological structure of trigonometric framework lattice, generates triangle according to level 0 topological structure and controls The level 0 segmentation look-up table of grid, builds trigonometric framework lattice according to level 0 segmentation look-up table Ground floor topological structure, and according to ground floor topological structure generate trigonometric framework lattice first Layer segmentation look-up table；

(3) recursion successively, obtains the n-th layer segmentation of trigonometric framework lattice search until building Table and n-th layer topological structure, wherein n is equal to the maximum segmentation number of plies set；

(4) position of each layer segmentation look-up table and level 0 control vertex is uploaded to GPU, The tinter that calculates of GPU segments look-up table and the position of last layer control vertex according to each layer, It is calculated the position of each layer control vertex successively；

(5) control of each original dough sheet in this topological structure is constructed according to each etale topology structure Dough sheet controls dough sheet as this layer, and determines that each controls the parameter field of dough sheet, specific as follows:

(5-1) will be each according to the segmentation number of plies residing for each original dough sheet in described topological structure Individual original dough sheet is divided into ordinary dough sheet and non-trivial dough sheet:

If the segmentation number of plies of the adjacent original dough sheet in the limit of current original dough sheet is respectively less than or is equal to work as The segmentation number of plies of front original dough sheet, the most current original dough sheet is ordinary dough sheet,

Otherwise, current original dough sheet is non-trivial dough sheet；

If (5-2) current original dough sheet is ordinary dough sheet, then with a ring of current original dough sheet The vertex index of neighborhood is as the control dough sheet of current original dough sheet, and determines this control dough sheet Parameter field；

If current original dough sheet is non-trivial dough sheet, then proceed as follows:

(5-21) ought more than the segmentation number of plies of current original dough sheet according to the adjacent original dough sheet in limit Front original dough sheet is divided into some sub-dough sheets,

(5-22) using the vertex index of a ring neighborhood of current original dough sheet as each sub-dough sheet Control dough sheet, and determine each control dough sheet parameter field；

(6) currently segment the number of plies according to Global Subdivision parameter determination, control according to each layer respectively The position on summit, each layer control dough sheet and each parameter field of dough sheet that controls by tessellation Tinter drafting level 0 dough sheet is to g_depth aspect sheet, and g_depth is for currently segmenting the number of plies.

2. the Loop subdivision of adaptivity based on irregular area as claimed in claim 1 The method for drafting of curved surface, it is characterised in that in described step (1), the maximum segmentation number of plies is with complete Office's subdivision parameter meets following condition:

1.0≤g_tessfactor≤2ⁿ,

Wherein, g_tessfactor is Global Subdivision parameter, and n is the maximum segmentation number of plies.

3. the Loop subdivision of adaptivity based on irregular area as claimed in claim 2 The method for drafting of curved surface, it is characterised in that described irregular area is trigonometric framework lattice Singular point, half acute vertex and in-edit by different level.

4. the Loop subdivision of adaptivity based on irregular area as claimed in claim 3 The method for drafting of curved surface, it is characterised in that described segmentation look-up table includes edge point table and puts point Table,

Described edge point table is for recording in irregular area adjacent the two of each limit, edge point place The index on four summits of individual triangle；

Described some point table is for recording the index on each summit in irregular area, and each pushes up The degree of point, and a ring neighborhood vertex index on each summit and the original position on a ring neighborhood summit.

5. the Loop subdivision of adaptivity based on irregular area as claimed in claim 4 The method for drafting of curved surface, it is characterised in that described control vertex includes edge point and summit.

6. the Loop subdivision of adaptivity based on irregular area as claimed in claim 5 The method for drafting of curved surface, it is characterised in that calculate the position of control vertex in described step (4) In calculating tinter, edge point thread and some point thread, described edge point thread it is respectively provided with when putting For calculating the position of edge point, described some point thread is for calculating the position on summit.

7. the Loop subdivision of adaptivity based on irregular area as claimed in claim 6 The method for drafting of curved surface, it is characterised in that described step (5-21) including:

If a the adjacent original dough sheet in () only one of which limit is more than the segmentation number of plies of current original dough sheet, With the adjacent original dough sheet in this limit and the midpoint of the common edge of current original dough sheet with this is the most original In dough sheet, the line on the summit that this common edge is relative is cut-off rule, is split as by current original dough sheet Two sub-dough sheets；

If b () has two adjacent original dough sheets in limit segmentation number of plies more than current original dough sheet, With the line at two adjacent original dough sheets in limit and the midpoint of the common edge of current original dough sheet and times The meaning midpoint of one common edge and the line relative with this common edge be cut-off rule will be the most original Dough sheet is split as three sub-dough sheets；

If c () has three adjacent original dough sheets in limit segmentation number of plies more than current original dough sheet, With the line two-by-two at the midpoint on three limits of current original dough sheet as cut-off rule, will the most original Sheet is split as four sub-dough sheets.

8. the Loop subdivision of adaptivity based on irregular area as claimed in claim 7 The method for drafting of curved surface, it is characterised in that described step (6) comprises the following steps:

(6-1) according to formula:

Determining and currently segment the number of plies, wherein g_depth is for currently to segment the number of plies, and g_tessfactor is Global Subdivision parameter,Represent log₂G_tessfactor rounds up；

(6-2) according to formula:

tessfactor_i+1=tessfactr_i/ 2,

Calculate the subdivision parameter of i+1 layer, wherein tessfactor_iIt is the subdivision parameter of i-th layer, I=0,1 ..., g_depth, wherein tessfactor₀=g_tessfactor；

(6-3) based on four box spline basic functions, according to subdivision parameter, the control of each layer Summit, control dough sheet and each parameter field controlling dough sheet draw the dough sheet of equivalent layer.